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High winds and Atypical Myopathy

Have you got a sycamore tree near your paddock? If so, be aware that during high winds at this time of year, sycamore seeds can pose a serious threat of Atypical Myopathy to the health of your horse.

AM (aka seasonal pasture myopathy, sycamore myopathy or sycamore poisoning) is caused by the toxin hypoglycin A, found in the seeds of a sycamore tree. This disease is not contagious and can affect all breeds, with young horses at greater risk. Affected horses can become quiet and lethargic for a few days before more severe signs appear.

What are the signs we should be looking out for?

  • Fatigue and lethargy
  • Reduced appetite
  • Shivering, sweating and trembling
  • Reluctance to move or recumbency
  • Muscle weakness and stiffness
  • Fine muscles tremors
  • Dark discoloured urine
  • High heart rate
  • Difficulty breathing and high respiratory rate


Horses don’t generally favour sycamore seeds but run the risk of ingesting them in sparce paddocks with additional debris such as dead leaves and wood with no supplementary feed.

We strongly advise owners on the following:

  • Restrict access to risky areas by using temporary fencing
  • Try not to use high-risk fields especially during high-risk periods
  • Regular checks of high-risk fields
  • Pick up and remove sycamore seeds, if possible
  • Provide supplementary feed to avoid temptation
  • No wet hay left on the ground as it will rot and trap seeds
  • Beware that high winds and floods can spread seeds
  • Avoid pruning seed laden trees as this can lead to mass pasture contamination
  • Limit grazing time (less than 6hrs) on risky fields
  • Rotate pastures to avoid overgrazing
  • Seek advice from your vet ASAP if you suspect sycamore seed ingestion

Remember: If you have any concerns or questions regarding Atypical Myopathy, please don’t hesitate to ring the team on 01323 815120